fix: plugins/app-backend/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-TARFS-10293725

Author: snyk-io[bot]

plugins/app-backend/package.json

@@ -45,10 +45,10 @@
     "clean": "backstage-cli package clean"
   },
   "dependencies": {
-    "@backstage/backend-common": "workspace:^",
-    "@backstage/backend-plugin-api": "workspace:^",
+    "@backstage/backend-common": "0.24.1",
+    "@backstage/backend-plugin-api": "0.6.19",
     "@backstage/config": "workspace:^",
-    "@backstage/config-loader": "workspace:^",
+    "@backstage/config-loader": "0.1.1",
     "@backstage/types": "workspace:^",
     "@types/express": "^4.17.6",
     "express": "^4.17.1",